It is known from WO 01/59891 A2, for example, to control radiation sources based on gas discharges by comparing a mean pulse energy or radiation dose with a corresponding reference value in order that an electric voltage, as discharge voltage, is adjusted by way of feedback such that deviations of the mean pulse energy or mean radiation dose from the reference value are minimized as far as possible.
Aside from pulse-to-pulse fluctuations, gradual deviations can also occur over a certain quantity of pulses. This drift, as it is called, may be caused, for example, by heating of components of the EUV radiation source and/or by wear of the components, for example, erosion of electrodes, depletion of the buffer gas, and so on.
If these drift-related deviations are offset by the control principle outlined above, the problem arises that increasingly larger deviations must be corrected with progressive drift. This imposes greater demands on the required measuring and control technology. In addition, as the deviations to be corrected increase, the absolute errors during the controlling process also increase, which is detrimental to a pulse-to-pulse stability of the EUV radiation.